The invention relates to a draft protection device for a balance, and it also relates to a balance that is equipped with the draft protection device.
The degree of precision that a balance delivers depends on a variety of factors. Of significance are air drafts which during a measurement are acting on the balance pan inside the weighing compartment. Therefore, to avoid undesirable air drafts, balances are in most cases equipped with devices that protect the weighing compartment from the undesirable effects of air drafts.
A draft protection device performing this function is known, e.g., from reference [1], Swiss Patent CH-677 029 A5. The draft protection device described in this reference consists of four or more wall parts that are hinged together. At least one of the wall parts has a U-profiled frame with a plate or windowpane that is slid into the frame so that it can be removed if necessary, for example to perform a so-called weighing-in procedure, or in general to put objects or materials on the balance in order to weigh them. In addition, a lid is hinged at the upper border of the wall part that forms the rear wall of the weighing compartment, offering an additional opening for access to the weighing compartment.
A further draft protection device, disclosed in reference [2], Swiss Patent CH-687 836 A5, is proposed for balances that have a support base, a fixed rear wall connected to the support base, and a front window panel connected to the rear wall by struts. In addition, there are two sliding doors constituting the side walls of the weighing compartment. In the area of their anterior edges, the sliding doors have guide means that reach around linear guiding elements located below the sliding doors.
Reference [3], published German Patent Application DE 198 49 399 A1, discloses a draft protection device that can be releasably connected to the base of a balance by means of a locking device. This draft protection device also offers a simple way of exchanging the draft shield panels, which makes the draft protection device easy to clean.
The known state of the art further includes draft protection devices with motor-actuated elements as disclosed in references [4] and [5], published German Patent Applications DE 37 41 313 A1 and DE 199 48 754 A1.
The device described in [4] has a t least two cylindrically curved wall elements that are movable relative to each other for opening and closing the weighing compartment. The device disclosed in reference [5] has at least two wall elements that can be moved independently of each other by a motorized drive mechanism.
In all of the draft protection devices described in the aforementioned references, the walls surrounding the weighing compartment, in particular the rear wall, are either made of a non-transparent material such as metal, or they consist of a transparent material, preferably glass.
However, a wall that is impassable to the outside light can darken the weighing compartment, while a transparent glass wall has the disadvantage that objects behind the balance are in full view of the operator of the balance, whereby the operator can be distracted from the actual weighing process.